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Perhaps that's because sailboats weren't designed by pilots. :D

Sort of. But crossing the proton streams brings the entire universe to a violent end, while short-changing the universe on energy makes the gods focus their anger directly at you. Now technically, I have diplomatic immunity from the laws of physics, but I still try not to violate them...

When it comes to energy bookkeeping, we are very careful to never short change the universe. It's considered very bad form. :D

You'll have to let us know how it goes convincing others. Some accept it relatively quickly, and some never will.

What you see on the nose is a sort of home made protractor. We were trying several methods to make sure I kept the cart steered directly downwind. I had a piece of yarn tied at the top of that pole and I used the protractor to make sure it was centered. There was also a camera at the base of...

No doubt. On the Volvo around the world race, his team had two boats. The partner boat lost a man overboard. They recovered his body (too late), and spent the next two weeks transporting the body to the next port. He's been on board for de-mastings, pitch-poles, and general major mechanical...

I used to windsurf, and now mostly kitesurf. I'm not qualified to sail anything much more than a Sunfish. But the guy that hired me into my current job has won more world records than I can count. He recently won two separate "round the world" races, and just won "Yachtsman of the year"...

Interestingly, as fast as those cats are (about 35 mph), they're not nearly as fast as the overall water speed record for sailing. That record is closer to 60 mph now (it's gone between sailboats, kiteboards, and windsurfers several times now). I'm pretty sure I've hit 35 on my kiteboard many...

This is the vector diagram for an ice-boat that’s maintaining a course such that its downwind velocity component is faster than the wind. I've assumed a boat going 45 degrees downwind at a speed of twice the wind speed. The ticket is to then compute the necessary L/D of the sail and keel to make...

It is true. In the last Americas Cup race Ellison's downwind leg beat the wind by a factor of about 2X. Ice boats and land yachts do it absolutely routinely. I understand they can achieve a downwind VMG (velocity made good) up to 4X or 5X. It's easy to show how that works with a quick...

Thanks. We can do a similar analysis for the upwind run if you want. The real difference is that we lose the prop and replace it with a turbine. Now instead of the wheels turning the prop, the turbine turns the wheels. The interesting thing is that the turbine is constrained by the Betz...

See above. I decided to knock out the drag equation while wasting time on a conference call. Incidentally, 5 meters/sec is about 11.2 mph (through the air), or 22.4 mph over the ground. Not screaming fast by any means, but not all that much slower than our record run. Our fastest run was...

OK, let's do the aerodynamic drag... Drag = 1/2 * rho * V^2 x Cd * reference_area Rho is air density: 1.2 kg/m^3 V is airspeed: 5 meters/sec Cd is our coefficient of drag: 0.25 reference area = 2 meter^2 So: Drag = 1/2 x 1.2 x 5^2 * .25 * 2.0 Drag = 7.5 Newtons. Therefore...

OK. So we're towing the Blackbird downwind at twice wind speed. We've got 200 Newtons of drag because the wheels are turning a generator. After generator losses, electric motor losses, and prop losses, we're getting 291.6 Newtons of thrust. Now we have to consider rolling resistance...

You guys are used to short props at high RPM, putting out lots of thrust. That is inefficient for the same reason stubby wings are inefficient. That's why sailplanes have such long skinny wings, and also why we have a 17.5 foot prop on the blackbird spinning 1/10th as fast as the props on your...

Great. Now let's take that 1800 watts and use it to turn the electric motor that's turning the prop. And let's make that motor 90% efficient as well. That means the shaft power on that motor will be given by: output_power = input_power x motor_efficiency output_power = 1800 watts * 0.90...

Good catch - you caught me in a mistake. I went back and edited it. Now using the original numbers throughout. Check me again and let me know if we're good. Updated numbers: Tailwind 5 meters/sec Ground speed: 10 meters/sec Retarding force on wheels: 200 Newtons Generator efficiency...

Excellent. Next step... instead of using a chain and sprockets for a transmission, we're going to use a generator on the wheels and an electric motor to turn the prop. This will make it easier to follow the energy flow. OK? So let's assume we have a tailwind of 5 meters/second (around 10...

No worries. Nope - I think you agreed that we can walk through the analysis together - step-by-step; making sure that I don't make any jumps you don't agree with. I'm just waiting for an answer to the first step in the analysis. This is it... For now, I don't wish to address the issue...

Yes. We talked about using a spinnaker or drogue 'chute that could be stowed as we approached wind speed. We also considered making big hinged panels that swing out from our pylons, and then automatically fold back as we pass wind speed. Ultimately we decided to keep it simple and use more...